The present invention relates generally to edge working machines for working sheet metal and particularly relates to the construction of a hold down device for such machines.
The careful working of the edges of sheet metal or a plate is one of the most important steps in the process for the manufacture of large pipes. The quality of the working of the plate edges is an optimum when the sheet metal is clamped as close as possible to the edge to be worked upon its support. For this purpose it is known to provide a plurality of hydraulic cylinders which, in turn, have plate-shaped or disk-shaped hold down devices at the end of each piston facing the metal plate. Furthermore, it is known to provide a plurality of hold down beams along the edge, and each beam is pressed upon the metal plate, sheet, etc., by two cylinders.
The invention relates specifically to improvements of such a hold down device having several elements such as beams. The known hold down beam is actuated by means of two cylinders having a point of contact in the region of the ends of the beam. The two cylinders can only be fully loaded when the hold down beam rests with its entire length upon the plate. However, usually plates or sheets of different lengths must be worked. Therefore, the danger exists that a plate or sheet metal, when introduced into the edge working (planing) machine, is not securely clamped at one or the other or even both of the end regions. This is particularly disadvantageous when, as happens frequently, the sheet metal plate at the end portion not securely clamped is capable of lifting slightly from the base.